Adhesive bonds that can be debonded again are increasingly important in various technological fields. Examples are the detachment of components within the framework of automated manufacturing processes, the repair of complex components with adhesively bonded subcomponents or the simplification of the separation of materials when recycling such components at the end of the product's life. The debonding of adhesive bonds can be achieved on demand by significantly reducing the strength of the adhesive bond layer e.g. by heating.
Thus, DE 198 32 629 A1 describes an adhesive system for forming reversible adhesive bonds based on polyurethanes, polyureas or epoxy resins, in which an additional component can be activated by introducing energy such that a degradation of the adhesive components takes place. For example, organic bases or acids which degrade the adhesive resin can be released from blocked precursors by introducing heat or radiation energy.
WO 2010/128042 A1 describes industrial adhesive compositions for debondable adhesive bonds for aircraft or motor vehicle construction which consist of a customary adhesive matrix and a particulate expansion material such as e.g. azodicarbonamide. The components are debonded by heating the adhesive bond at least to the expansion temperature of the expansion material.
In dentistry, the debonding of adhesive bonds is important among other things in orthodontics, where brackets which are adhesively bonded to the tooth surface to correct malocclusions must be removed again without damaging the tooth enamel after successful correction. Moreover, in case of repair or complete replacement of high-strength ceramic restorations or crowns, which are laborious to remove mechanically, cement bonds that can be easily softened or separated would be advantageous.
In connection with orthodontic applications, US 2007/0142498 A1 describes dental compositions which contain thermally controllable additives such as e.g. thermoplastic polymers.
US 2007/0142497 A1 describes dental compositions based on dimethacrylates with acid-labile tertiary carbonate groups and photoacids such as e.g. triarylsulfonium salts. These compositions can be photochemically cured using light in the visible range with suitable initiators such as, for instance, the bisacyl phosphine oxide Irgacure 819 (photobonding) and softened again by irradiation with UV light at increased temperature (photothermal debonding).
WO 2013/034777 A2 describes dental materials which contain polymerizable compounds with a thermolabile or photolabile group such as a thermolabile Diels-Alder group. However, it was found that these materials must be exposed to relatively high temperatures of typically more than 100° C. in order to bring about a sufficiently rapid softening.